There are known conventional illumination devices, such as vehicle lighting fixtures, that include a light guiding lens that is capable of emitting light along its surface.
Japanese Patent Application Laid-Open No. 2014-041787 describes this type of illumination device. The disclosed illumination device includes a plate-shaped light guiding lens having a rod-shaped light guiding portion extending along the light guiding lens at one end side. The light guiding portion is integrally provided to the light guiding lens. The illumination device further includes a light source, such as a light emitting diode, disposed to face to one end face of the light guiding portion. With this configuration, light emitted from the light source can be incident on the end face to enter the light guiding portion, and be guided thereinside to enter the plate-shaped light guiding lens, thereby allowing the main surface of the light guiding lens to project light.
Since the rod-shaped light guiding portion is integrally connected to the light guiding lens that serves as a light emission portion, the light that is emitted from the light source and just enters the light guiding portion through the end face is likely to directly enter the light guiding lens near the end face. This prevents the light from being sufficiently guided to the opposite end of the light guiding portion, resulting in luminance unevenness.
Japanese Patent Application Laid-Open No. 2014-157804 discloses an illumination device including a light guiding lens with a light guiding portion where there is a gap (air layer) provided between the light guiding portion and the light guiding lens. This can facilitate the light guiding to the opposite tip end of the light guiding portion to suppress the luminance unevenness of the light guiding lens.
However, in this case where there is a gap provided between the light guiding portion and the light guiding lens (serving as a light emission portion), luminous flux may be lost (luminous flux loss) when the light from the light guiding portion enters the light guiding lens via the air gap. Thus, the luminous flux utilization efficiency may deteriorate.